Bonded abrasives



Patented May 7, 1946.

. 'z,40o,o36 UNITED STATES PATENTJOFFICE BONDED ABRASIVES Charles E. Wooddell, Garret Van Nimwegen, and

Edward T. .Hager, Niagara Falls, N. Y., as-

signers to The Carborundnm Company, Niagara Falls, N. Y., a corporation of Delaware No Drawing. Application April 15, 1944,

v Serial No. 531,280

6 Claims. (01. 51-298) This invention relates to new and improved abrasive articles and to the making of the same. More particularly, the invention relates to abrasive articles characterized in the art as elastic bonded abrasives, of which rubber-bonded abrasives are an example.

This application is a continuation-in-part of application Serial No. 438,814, filed April 13, 1942.

While rubber-bonded abrasive articles have many desirable properties and, can be manufactured in comparatively short periods of time, it is difficult to obtain natural rubber of consistent quality from time to time. Natural rubber is obtained from many species of plants such as Hevea brasiliensis, Castillo elastica, Manihot, the guayule species, etc. Commercial rubber obtained from such different species by various methods is a somewhat indefinite mixture of resins, rubber hydrocarbon and proteins. The general formula for the rubber hydrocarbon is (mm, where n represents the degree of polymerization. The properties of commercial rubber vary with the source of the rubber latex, with the methods used to coagulate the latex, and with the methods used to remove undesirable resins and proteins from the rubber mass.

A great deal of research has been undertaken with the object of using asynthetic polymerization product which might be vulcanizable and have the desirable properties of natural vulcanized rubber. and fewer of its disadvantages in the In accordance with the present invention we use as a bond for abrasive articles a synthetic polymerization product which is vulcanizable to a state or condition similar to that of a vulcanized hard rubber or ebonite. Such vulcanizable polymerization products are obtained by co-polymerizing butadiene, or one of its homologs or analogs, in admixture with one or more secondary monomers that will co-polymerize therewith, the secondary polymerizing component functioning as a hardening monomer whereby the final polymerized, hard vulcanized bond is obtained. The bond of the present invention is the vulcanized polymeriaztion product obtained after blending or compounding otthe previously polymerized co-polymer with the necessary vulcanizers, accel erators, fillers, activators, etc., and vulcanization therewith, the co-polymer being a polymerized product comprising (1) One or more monomers of the butadiene type, and

(2) One or more secondary monomers of a hardening type.

Monomers of butadiene, its homologs and analogs, are characterized by the presence within the monomer of two unsaturated bonds in conmaking of bonded abrasive wheels. 'It has been suggested for example that a synthetic polymer known briefly as chloroprene should be used in the manufacture of abrasive articles. Chloroprene o1 2-chlorobutadiene can be readily polymerized. By interrupting the process of polymerization before completion, an alpha polymer of chloroprene is obtained which is soft, plastic and soluble in benzene. The product resembles unvulcanized rubber in its physical properties and mechanical behavior. At 130 C. the alpha polymer changes into an elastic polymer in a few minutes. Catalysts such as zinc oxide accelerate this change to the elastic chloroprene. Sulphur is not necessary to bring about this change. By suitably compounding and curing chloroprene, vulcanizates can be obtained with tensile strengths of over 3000 pounds per square inch. Elongations at the breaking point are obtained of the order of 700 to 900 per cent. Efforts have been made to obtain a vulcanizate similar to hard rubber. This does not appear to be possible by th polymerization of chloroprene. These properties of polymerized chloroprene greatly limit its usefulnessas a bond for abrasive articles. With elongations of the order of magnitude of 700 to 900 per cent, abrasive grain cannot be held securely enough by a chloroprene bond to make grinding wheels for processing hard materials.

jugated position. The existence of the two points of unsaturation makes it possible to more readily produce a polymerized form of the substance with itself and other monomers, and at the same time leave sufficient remaining points of unsaturation to permit vulcanization and provide a source of cross-linkage and interaction with the variousother constituents of the mixture, thereby obtaining an ultimate bond of high strength, hardness and durability.

For example, butadiene monomer has the formula CH2=CH-CH=CH2, in which there are two double bonds, one between the first and second carbon atoms of the chain and the second double bond between the third and fourth carbon atoms of the chain. These double bonds are points of unsaturation, inother words, they are points in the molecule where other butadiene molecules or other chemical molecules may attach themselves or interact with the butadiene molecules to form a more complex, but modified substance. The above monomeric butadiene is considered for purposes of the polymerization reaction to take the formula form as follows;

which, as can be seen provides two free available merized substance double bonds, or points of unsaturation, at which the polymer can link itself to other modifying constituents or by means of vulcanization agents form cross-linkages to form hard vulcanizates. Monomers of the butadiene type, i. e., homologs and analogs of butadiene, which can be used, include butadiene, isoprene, chloroprene, dimethyl butadiene, divinyl ether and vinyl acetylene.

The copolymerizing material for use in conjunction with the butadiene type monomer is one which is compatible with the butadiene or other dioiefinic constituent and will copolymerize therewith to provide a co-polymer which will vulcanize to the hard state, for which reason we refer to the secondary part of the co-polymer as a hardening monomer. such materials have at least one, and sometimes more than one, unsaturated bond, in the monomeric form. Acrylic nitrile monomer has been found to be highly satisfactory for copolymerizing with butadiene to ob; tain a butadiene-acrylic nitril polymerization product which is vulcanizable to a hard, rigid condition of the character essential to make a good abrasive bond. Other hardening monomers which can be used include styrene, binylidene chloride, acrylic and methacrylic acid esters, halogen-substituted acrylic and methacrylic esters, halogen-substituted olefinic compounds containing a co-polymers may also be modified by admixingother polymeric compounds, one example of a satisfactory polymerization product so modified being butadiene-acrylic nitrile co-polymer blended with to 70 percent of a vinyl chloride polymer.

By means of emulsion polymerization of butadiene and the copolymerizing material an interpolymer can be obtained in the viscous form. For example, co-polymers of butadiene and styrene or acrylic nitrile can be so made in proporequivalent vulcanizing agent, a filler (or reinforcer) such as hard rubber dust, or reinforcing clays, vulcanizing accelerators, antioxidants or other activating or protective ingredients which may be required. This bonding mixture is then admixed with abrasive particles in the desired proportions. The abrasive mix is made by any suitable means at a temperature sufliciently low to retard further polymerization and is then transferred to molds. The molded articles can be cured at temperatures of about 340 F. in-90- 120 minutes.

The following is a typical abrasive mix in which a butadiene-acrylic nitrile polymerization product, when vulcanized, constitutes the bond for the abrasive granules. The procedure for its use is given in detail.

Parts by weight Butadiene-acrylic nitrile co-polymer 100.0 Dibutoxyethylphthalate' 50.0 Phenolic resin 12.0 Sulphur 40.0 Benzothiazyi disulphide 1.0 Zinc oxide 5.0 Cryolite 300.0 Abrasive grain 1230.0

The bond is prepared before any abrasive grain is incorporated in the mix. The mixing operation is carried out on a pair of ordinary rubber rolls. The butadiene-acrylic nitrile co-polymer is passed through the cool rolls three or four times and then allowed to run around the front roll during the b eaking down period. The accelerator is adde with cutting and blending. The

' softener and phenolic resin, followed by the zinc tions ranging from to 75% of butadiene to 40-25% by weight of the styrene or acrylic nitrile. The viscous form so obtained may be further treated to give the sheet form.

As a further example, co-polymers of butadiene and vinylidene chloride can be made in proportions ranging from about 50 to of butadiene to about 50-35% by weight of the vinylidene chloride.

If the co-polymer is used in sheet form it should be plasticized by milling and by the addition of softeners or plasticizers. The desired softener may be the. ester type such as dibutoxyethylphthalate, dibutylphthalate or tricresylphosphate. It may also be one of the soft coal tars, coal tar products or cumar resins. A combination of these different softeners is often advisable.

After the synthetic oo-polymer has been obto a plastic mass, it is mixed with sulphur or an oxide and filler, are incorporated slowly with further working of the mix. The sulphur is the last ingredient added and is-introduced without cutting. After thorough mixing the batch is out each way several times before removing it from the rolls.

The rolls are made slightly warm and the bond mixture is passed through the rolls to make it more plastic before the addition of abrasive. The abrasive is added to the mix in small amounts in the manner employed in making natural rubber bonded abrasives. When all the abrasive has been added the abrasive-bond mixture is sheeted to the desired thickness and finally died out in the required shape before vulcanization. The wheels are cured two hours at 80 pounds steam and 500 pounds per square inch pressure in a mold and later finally vulcanized 16 hours at 300 F. in an oven.

An advantage of the invention is that synthetic polymerization products can be obtained according to specification as materials of more-definite properties than commercial natural rubber which as noted earlier contains different percentages of resins and proteins, which are difilcult to separate completely from the rubber hydrocarbon. Oi extreme importance to the inventions is the fact that the polymerization products herein used are capable of vulcanization to various stages of resiliency and hardness, even to the substantially rigid condition of hard rubber or ebonite.

Generally speaking, the vulcanizates herein referred to are characterized by a higher thermal conductivity than natural rubber, especially good heat resistance and an ability to resist deterioration by numerous oils and hydrocarbons, which are often used in wet grinding operations.

A number of changes can be made in the menufacture of abrasive articles and in the choice of polymerization products and modifying ingredients from the specific example which has been described by way of example without departing from the invention which is defined within the compass of the following claims.

We claim:

1. A bonded abrasive article comprising abrasive particles and a co-polymer of butadiene withvinylidene chloride, said co-polymer being vulcanized to a substantially rigid condition.

2. A bonded abrasive article comprising abrasive particles and a co-polymer of a dioleflnic monome with a halogen-substituted oleilnic compound, said co-polymer being vulcanized a substantially rigid condition.

3. A bonded abrasive article comprising abrasive particles and a co-polymer of a butadiene homolog with vinylidene chloride, said co-polymer being vulcanized to a substantially rigid condition.

18 condition.

4. A bonded abrasive article comprising abrasive particles and a co-polymer of a dioleflnic monomer with a halogen-substituted vinylcompound, said co-polymer being vulcanized to a substantially rigid condition.

5. A bonded abrasive article comprising abra- I sive particles and a binder therefor, said binder comprising butadiene copolymerized with-35-50% vinylidene chloride, said binder being vulcanized CHARLES E. WOODDELL. GARRET VAN NIMWEGEN. EDWARD T. HAGER. 

